1. Field of the Invention
The present invention relates to a system for vacuuming out sediment from a potable gravity water tank or tower without any disruption in service.
2. Brief Description of the Prior Art
Most water storage tanks and towers are not designed to be cleaned and have no “drain pipe” or “washout pipe.” But the fact is that all water tanks and towers accumulate sediment in time which becomes a safe habitat for bacteria, protozoa and viruses. In time, the layer of sediment can grow from inches to several feet thick. This is health problem because water flows in and out of the tank through the same pipe in the bottom hence we drink from the bottom of the tank. In addition to being a health risk, sedimentation promotes electrolytic corrosion which naturally occurs in metal tanks over time due to electrical imbalances between the water and the conductive tank material. While water tanks are painted to resist corrosion, sedimentation promotes the passage of electrical current between the negatively charged metal and positively charged water, which can eat through the paint. While corrosion poses no threat to water quality, it does pose a threat to a tower's structural integrity at the bottom of the water tank which is subjected to the greatest pressure and where corrosion can least be afforded.
While some states require water storage tanks and towers to be inspected, only Florida requires them to be cleaned. Inspection and cleaning are not the same. Inspection may consist of putting an underwater camera inside the tank to check for structural soundness of the roof and walls and for the condition of the paint without paying attention to the sediment on the floor. Traditionally cleaning has required draining the tank or tower and sending a crew inside with buckets and shovels. Shovels are hard on the painted surface and even the most dedicated crew cannot get cannot get all of the sediment off the floor.
Another way to clean out a tank or tower is with a pressure washer which also requires draining the tank. Workers are sent into the tank where they flush the sediment down the water inlet pipe as there is no where else for it to go. Hence the sediment that is flushed down the pipe is pumped right back up into the tank when the tank or tower is put back into service. Both the bucket and shovel method and pressure washing require putting the tank or tower out of service for some period of time.
Presently, the only way to clean out the sediment without disrupting service is by sending a diver into the tank. To keep the water potable, the diver must be washed down with a chlorine solution. The diver can then enter the tank or tower and vacuum loose sediment from the floor. This leaves the tank much cleaner than pressure washing or the tradition bucket and shovel method but it is dangerous, requires equipment that is only used in potable water and expensive. It is also not legal in some states.
Municipal budgets are frequently stretched in poorer or less populated communities and since tank and tower cleaning is not federally or state mandated, not done. Elected officials may vote to clean or repaint the exterior of a water tank or tower without considering the inside condition, as out of sight is out of mind, but serious illnesses may occur when an event scours disease laden sediment into the distribution system (e.g., fire flow, poor operation, power outages, etc.) and sediment presents a health hazard to susceptible individuals at all times and a risk to the public in general. In addition, sediment also promotes electrolytic corrosion in the bottom of the tank which may put the tower at risk of rusting through.